1. Technical Field
This invention relates to a rotation connection unit, for example, being built in a steering system of an automobile for use as means for connecting circuit wiring of a steering wheel side (rotation side) and a body side (fixed side).
2. Related Arts
Hitherto, as this kind of rotation connection unit, a swirl type wherein a belt-like cable for conduction, which normally is called a flat cable and will be hereinafter called simply cable, is wound like a swirl in a cable housing space and an inversion type wherein the winding direction of the cable is inverted at an intermediate point have been known.
An inversion-type rotation connection unit taking an inversion-type multiple-winding structure of housing two or more cables in response to an increase in the number of circuits to be connected is also known.
FIG. 8 is a sectional view of a rotation connection unit in a related art and FIG. 9 is a front view of only cables in the rotation connection unit in the related art. Here, a double-winding structure using two flat cables is taken as an example and the case where the rotation connection unit is built in a steering system of an automobile is illustrated.
In the figures, numeral 101 denotes a case as a cylindrical outer member fixed to the body side of the automobile and numeral 102 denotes a rotor as an inner member rotated in one piece with a steering shaft. A cable housing space 103 is formed between the case 101 and the rotor 102. Two cables (a first cable and a second cable) 104 and 105 are housed in the cable housing space 103 in such a manner that they are wound and that the cable winding direction is inverted at an intermediate point.
A guide ring 106 for movably guiding both the cables 104 and 105 has guide grooves 107 and 108 at two parts in a circumferential direction (usually, symmetrical two parts spaced 180 degrees from each other as shown in the figure). An inversion part 104a of the first cable 104 is passed through one guide groove 107 (first guide groove) and an inversion part 105a of the second cable 105 is passed through the other guide groove 108 (second guide groove).
Both the cables 104 and 105 have inner peripheral terminals fixed to the rotor 102 by inner peripheral terminal members 109 and 110 and outer peripheral terminals fixed to the case 101 by outer peripheral terminal members 111 and 112.
The inner peripheral terminal members 109 and 110 and the outer peripheral terminal members 111 and 112 are placed at the same position or different positions with respect to both the cables 104 and 105. In the example shown in the figure, the inner peripheral terminal members 109 and 110 are placed at almost symmetrical positions with respect to the rotation center and the outer peripheral terminal members 111 and 112 are placed at the same position.
The inner peripheral terminal members 109 and 110 are housed separately in inner peripheral terminal spaces 113 and 114 provided swelling inwardly at two parts of the inner periphery of the rotor 102 and the outer peripheral terminal members 111 and 112 are housed together in an outer peripheral terminal space 115 provided swelling outwardly at one part of the outer periphery of the case 101. Outer wiring of the steering wheel side and outer winding of the body side are connected to the terminal members 109, 110, 111, and 112.
Problem to be Solved
However, in the rotation connection unit having the inversion-type double-winding structure, the following problems occur:
(1) When the steering wheel is turned at high speed, a discrepancy occurs between the rotation speed of the guide ring 106 and the move speed of cable""s inner and outer peripheral portions 104b, 104c, 105b, and 105c and a situation in which coming and going of the cable inversion part 104a, 105a relative to the guide groove 107, 108 is too late occurs.
In this case, a phenomenon in which the cable""s outer peripheral portions 104c and 105c stick to the guide ring 106 so as to fasten the guide ring 106 from the outer periphery occurs and accordingly it is feared that rotation resistance of the guide ring 106 may grow.
(2) Both the cables 104 and 105 differ in fixing positions of inner and outer peripheral terminals and thus are set to difference lengths. If the lengths vary because of manufacturing tolerances, a situation in which the length difference to be provided between both the cables shifts from the setup value occurs.
If such a situation occurs, the relative positions of the inversion parts 104a and 105a of both the cables 104 and 105 shift and thus either of them is hard to be well housed in the guide groove 107, 108 at the assembling time.
In this case, in the rotation connection unit in the related art having no flexibility of the cable length, there is little room for absorbing the cable length discrepancy from the setup value and thus it becomes difficult or impossible to assemble or as a result of forcibly passing the cable inversion parts 104a and 105a through the guide grooves 107 and 108, it is feared that smooth motion of the guide ring 106 may be hindered.
It is an object of the invention to provide a rotation connection unit for making it possible to provide the length of a cable outer peripheral portion with flexibility.
Means for Solving the Problem
According to the invention as in aspect 1, there is provided a rotation connection unit wherein an inner member and an outer member are fitted for relative rotation in a state in which a cable housing space is formed between the inner member and the outer member, wherein a plurality of conduction cables are housed in the cable housing space in a state in which the winding direction is inverted at an intermediate point and the cables move with relative rotation of both the members, and wherein a guide ring for guiding moving of the cables is placed rotatably and is formed with a plurality of guide grooves through which inversion parts of the cables are passed at different positions, characterized in that the cables are housed in the cable housing space in a state in which a force in a direction touching the inner periphery of the outer member is given.
According to the configuration, the cable is housed in the cable housing space in a state in which the force in the direction touching the inner periphery of the outer member is given, so that the cable outer peripheral portion can be changed with a constant margin. The length of the cable outer peripheral portion is thus provided with flexibility, whereby if the rotation connection unit is rotated at high speed, a phenomenon in which the cable outer peripheral portion sticks to the guide ring so as to fasten the guide ring 6 from the outer periphery does not occur, so that an increase in the rotation resistance of the guide ring can be prevented. Shift from the setup value caused by cable length manufacturing tolerances can be absorbed, assembling the rotation connection unit is facilitated, or smooth motion of the guide ring can be provided.
For example, as in aspect 2, the cable maybe formed longer than the length of the outer peripheral portion of the cable touching the outer periphery of the guide ring, whereby the force in the direction touching an inner periphery of the outer member is given.
Further, as in aspect 3, if the rotation connection unit comprises terminal position adjustment means for attaching a terminal member attached to a terminal of the cable to the outer member or the inner member so that the position of the terminal member can be adjusted in a length direction of the cable, the cable outer peripheral portion can be changed with a constant margin by adjusting the position of the terminal member.
For example, as in aspect 4, the terminal position adjustment means may comprise a plurality of engaged parts formed in the outer member or the inner member at predetermined pitches in the length direction of the cable and an engagement part which is formed on the terminal member and can engage at least one of the engaged parts.
Further, as in aspect 5, if the terminal member attached to the terminal of the cable is attached to the outer member or the inner member in a state in which it can be moved in the length direction of the cable and is elastically urged in a direction in which the cable touches the outer member, the cable outer peripheral portion can be changed with a constant margin as the terminal member is moved.
Further, as in aspect 6, if the cables are formed like springs in the terminal proximity portions, the cable outer peripheral portion can be changed with a constant margin as the cable itself becomes deformed.